Electrical control



April 26, 1960 J. s. BLAcKwELL 2,934,730

ELECTRICAL CONTROL Filed June 8. `1959 ATTORNEYS.

United States Patent Oiice 2,934,730 Patented Apr. 26, V1960 2,934,730 A ELECTRICAL CONTROL John S. Blackwell, Rutland, Vt., assguor to The Howe Scale Company, Rutland, Vt.

Application June 8, 1959, Serial No. 818,856

7 Claims. (Cl. S33-67) This invention relates to a securable memory device for electronic control systems. More particularly, it relates to such a securable memory device to be used as Athe control element in electronic control circuits for electronic weighing systems, and the like, as disclosed in the application for U.S. Letters Patent of William D. Macgeorge, Serial No. 657,639, tiled May 7, 1957, entitled Control Circuits; but it is not limited thereto.

In the control circuits disclosed in the above-described Macgeorge application and in other control circuits, which may be characterized as potential magnitude null balance systems, a reference potential is applied to the ends of a potentiometer or voltage divider and the voltage from a ixed or adjustable vtap of the potentiometer or voltage divider is balanced against a potential magnitude signal. In the most common type of such control circuits, the reference voltage and the signal voltage are produced by identical electromechanical transducers. The reference transducer is set to provide a constant potential to be applied to a series of potentiometers or voltage dividers of identical total impedance as abovedescribed, and the tap positions on the various potentiometers or voltage dividers correspond to the conclusion of a particular control operation. That is, when the voltage from the signal transducer is of the same magnitude as the voltage from the particular potentiometer or voltage divider tap then connected in circuit, this equivalence is detected by a null actuated relay and a switching operation takes place during which one controlled operation is concluded, another started, a new voltage divider or potentiometer tap introduced in circuit, and, as may or may not be the case, another transducer for the next operation may be introduced into the circuit. In such a system the positions of the voltage taps on the potentiometers or voltage dividers determine a certain formula of operations, and in the most versatile kind of system it is desired that, if potentiometers are used in the system, they be resettable for new and diiferent formulas as may be desired by the user.

However, when adjustable potentiometers are used, as

.disclosed in the above-described Macgeorge application,

system. One solution to this problem `which has been proposed, and is now in actual operation, is disclosed in the application for U.S. Letters Patent of Charles E. Roessler, Ir., entitled Printed Circuit Formula Card Systems and Their Components, which was tiled June 9, 1958, Serial No. 740,969. In that application there is described a system and apparatus for utilizing printed circuit formula cards to automatically set the formula desired by controlling the selection of voltage dividers. As disclosed in that application, a single printed circuit card corresponds to a single voltage divider or potentiometer and, in the case of weighing, corresponds to a single ingredient. However, there are certain inherent limitations in this system, such as the rather extensive relay circuitry and relatively complicated wiring required; Vand the fact that the formulas can be read off of the printed circuit card, thus presenting the user who has secret formulas with a rather diicult security problem. Also, since in the prior system there is a single printed circuit card for each ingredient, it is possible for the operator to accidentally interchange cards and thus cause an incorrect formula of operations to be performed.

The above-discussed problems are present in many forms of electronic control systems which require, for the setting of separate formulas, the setting of electrical or electronic memory devices. According to the present invention, the above problems are solved by employing as a securable memory device a small unitary plug-in element which contains control means that may be set for a particular formula and then sealed from further access. The unit is then plugged into the control panel of the control circuit whenever the particular formula contained therein is desired. Thus the present invention provides a relatively tamper-proof memory device, free from the problems of human error in repeatedly changing settings, and capable of preserving the secrecy of the .particular formula contained in the unit.

It is therefore an object of this invention to provide one-step formula setting in electronic control systems. Another object of the invention is to prevent errors in formula setting in electronic control systems. A further object of the invention is to provide objects of the above character and to save time and expense in formula setting for electronic control systems.

Still another object of the invention is to prevent tampering with formula settings in electronic systems. A further object of the invention is to provide objects of the above character and to protect secret formulas used in electronic control systems. A still further object of the invention is to provide the above objects conveniently and economically.

Another object of the invention is to provide a small, conveniently storable unit which will accomplish the above objects. And still another object of the invention is to provide an accurate securable memory device of the above character.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises an article of manufacture possessing the features, properties, and the relation of elements which will be exemplied in the article hereinafter described, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in conjunction with the accompanying drawing, in which:

Figure l is a perspective view of the preferred embodiment of the article of the present invention and illustrates its use as incorporated into the control panel of an electronic control system;

Figure 2 is a top View of the article of Figure l with a portion of the cover cut away to sho-w internal elements;

Figure 3 is an internal wiring diagram of the article of Figures l and 2, showing the connection of internal potentiometers to a printed circuit plugboard; and

Figure 4 is an end view of the article of Figure l.

Similar reference characters refer to similar elements throughout the several views of the drawing.

In general, the article of the present invention comprises a at parallelepiped enclosure having plural connector plug means projecting through one of its elongated rectangular faces for connection into a control circuit; a scalable sliding front cover or face plate onto which the formula number may be printed together with other information; and a plurality of settable miniature potentiometers, or any other settable electrical elements (herein generally called memory devices) contained within the enclosure; the enclosure being constructed so that internal access may only be afforded by removing a seal and opening the face plate.

More particularly, referring to Figure l, a control panel 12 has a socket 14 located therein which is adapted to receive the securable memory'device of the present invention, generally indicated at 16. A printed circuit board 18 having a plurality of connectors 20 printed thereon projects through the back face 22 of the memory device 16.

As shown in Figure 1, a face plate securing screw 24 has been removed from its normal position within a bore 26 in the front side 28 of the memory device 16. Also, a lead seal 30 has been broken so that a sliding face plate 32 may be slipped back along guide tracks 34, revealing an opening 35 in the front side 28 of the memory device 16 through which access is afforded to a plurality of minature potentiometers 36 and their respective screw heads 38 by means of which their resistance values may be set as desired.

Referring now to Figure 2, the printed circuit board 18 is mounted to the bottom member 54 of the device 16 by screws 40. The connectors 20 are located on the underside ofthe board 18. The minature potentiometers 36 are mounted on two parallel rails 42-42 which pass through openings (not shown) in each potentiometer. The potentiometers 36 are held in place by fasteners 44 which also are mounted on the parallel rails 42-42. Lead wires 46 of the potentiometers 36 are connected to the printed connectors 20 by soldering in the conventional manner. As can best be seen in Figure 3, the tap leads 46' of four of the potentiometers 36 are connected to a common connector 2li. This is because, for the particular memory device illustrated, there are five control operations corresponding to the five potentiometers 36, and four of these control operations involve a single signal transducer while the fifth involves another signal transducer. Thus the four upper potentiometers shown in Figure 3 may have their taps 46' all connected together and ordinarily would have the same total impedance.

Again referring to Figure 2, it can be seen that when the potentiometers 36 of the memory device 16 have been set by means of the setting screws 38 and the face plate 32 slid to its normal position, covering the front side 28, the face plate securing screw 24 may be passed through a securing screw aperture 48 of the face plate 32. Also, the lead seal 30 may be passed through a seal aperture Sil in the front plate 32 and also through a seal track 52 in the bottom member 54 of the memory device 16.

Referring now to Figure 4, the bottom member 54 and the upper member 56 of the memory device 16 are held together by four screws 58 (see also Figure 2). To insure that the memory device 16 is not opened without defacing same, the screws 58 are sealed with a hard plotting compound such as Glyptal in the spaces 60 above the screws 58.

It will be obvious to those skilled in the art that the inventive configuration of the article of the present invention may be adapted to use with any plurality of settable electrical elements when they are used as memory elements of an electronic control system.

A formula may be conveniently set into the article of the present invention in the following manner: The unit is plugged into the control system, and the first operation of the formula to be set is performed under manual control; the potentiometer or other electrical control element in the unit which is to control the first operation is then manually adjusted until an electrical null is obtained between the output of the control element and the signal transducer. (This null may be indicated by a lamp, controlled by the null actuated relay, or the operator may listen for the relay and switches controlled by it to operate.) The next operation is then performed manually and its control element set in the same manner; and so on for the rest of the formula of operations. Alternatively, a small null balance system may be constructed having calibrated signal and reference transducers identical to the control systern, and they may be manually adjusted to correspond to the conclusion Of each operation and the voltages of the system balanced by adjusting the control elements of the memory device. After the article of the present invention has been set, as outlined above or in any other convenient manner, it is closed and sealed and then may be used in the control system whenever its formula is required. If the formula is no longer required, the unit may be reset for a new formula.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above article without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense,

it is also to be understood that the claims following are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

l. In a securable memory device for use as a control element in electronic control systems comprising, in combination a plug-in unit of generally fiat parallelepiped configuration having a plurality of plug-in contacts extending through one side thereof, and adapted to be connected into the control system, a front plate movably mounted on the opposite side of said unit and having a normally closed position, a plurality of miniature adjustable potentiometers of generally elongated parallelepiped configuration longitudinally disposed within said container between said opposite faces, a plurality of connections located at one end of each of said potentiometers and connected to said contacts, each of said potentiometers having an adjustable setting screw at its end opposite said connections, each said screw adapted to vary the resistance characteristics of its associated potentiometer, said unit having an opening in said opposite side adapted to afford access from outside the unit to said setting screws when said front plate is moved from its normal position, and means for securing said front plate in its normally closed position to deny access to said adjustable potentiometers and their respective setting screws.

2. The article defined in claim 1 in which said securing means comprises a lead seal.

3. In a plug-in electrical device for use as the controlling element in a control circuit of an electronic system, the combination of a substantially parallelepiped container, a plurality of miniature potentiometers in the shape of elongated parallelepeds longitudinally disposed in and enclosed by said continer and each having electrical connectors at one side and an adjustable screw head at a second side thereof for preselecting the electrical characteristics of each potentiometer, a plurality of plug-in contacts passing through a first side of said container and electrically connected to said connectors, a second side of said container having an opening therein adjacent said screw heads to provide access thereto for adjusting said screw heads, and a face plate adapted to cover said opening, whereby a plurality of said devices may be interchangeably plugged into said control circuit to establish particular patterns of controlled operations.

. 4. The combination defined in claim 3 in which there is sealing means to seal said face plate in closed position.

5. The combination defined in claim 3 in which there is a bar mounted in said container crosswise of said potentiometers and connected to said potentiometers.

6. The combination defined in claim 3 in which there is a pair of spaced bars in said container extending cross- Wise of said potentiometers and interconnected therewith.

7. The combination defined in claim 5 in which said bar extends through apertures in the casings of said potentiometers to hold them in position.

References Cited in the le of this patent UNITED STATES PATENTS 

